While working in the diamond recovery field and supplying of diamond recovery technologies the problem of non-liberated and partly-liberated diamonds has been observed. Non-liberated diamonds are those still attached to rock product/particles/gravel such as Kimberlite and other minerals. These non-liberated diamonds can then in turn be misplaced in the beneficiation process, which can result in them being misplaced during dense media separation, DMS, due to their density being below the cut point of the DMS Cyclone and subsequently sent to the tailings.
Non-liberated diamonds can also be damaged/stressed or severely broken while in the circuit due to them not reporting to the recovery section of the plant, but then reporting to the crushing section and then in turn being broken as the size of the material is reduced to pass the CSS which then in turn damages the diamonds. This constitutes a preventable and unnecessary value loss for a mining company that is processing the deposit, and for the government that receives royalties and taxes on the sale of the diamonds.
Prior art diamond detection involves excitation by a laser beam and measurement of the laser light scattered by the crystalline structure of diamonds. By using the property of diamonds to scatter light within their crystalline structure and the effect of “Glowing” or “Lighting Up” the area around the direct reflection, it is possible to use this as a signature to discriminate the diamonds from rock product or particles/gravel such as Kim berlite and other minerals even if the diamond is only partly liberated and still attached to the gravel. The disadvantage of this basic principle is that other transmissive minerals like Quartz, some calcite etc. scatter as well and may be misplaced in a sorting process resulting in higher yield.
Other prior art documents describe other methods for detecting a target material in a material stream, such as the method described in EP2392414, which method involves illuminating a material stream with light having a pre-determined spectral bandwidth, said pre-determined bandwidth being in the proximity of the Full Width at Half Maximum value of the spectral peak of the target material that is to be detected; whereafter reflections and scattered light from the illumination means are captured and analyzed.
It is therefore an object of the invention to come up with a high-speed process for the improved recovery of partly liberated diamonds that would otherwise be damaged or lost. It is a further aim to improve diamond detection. It is a further aim to improve diamond value management by providing suitable diamond recovery technologies to suit a wider variety of ore types.
The object of the present invention is to overcome or alleviate at least one of the abovementioned problems. This is achieved by a method as defined in the independent claim. Advantageous embodiments of the present invention are derived from the subclaims and the following description.
It was surprisingly found that using at least one monochromatic SWIR laser beam can be advantageously used for recovery of partly liberated diamonds in a precise and reliable manner. This finding is surprising as choosing the bandwidth for the illuminating beam is usually done by taking the Full Width at Half Maximum value of the spectral peak of the target material that is to be detected. The rationale behind this is that the skilled person knows that a certain bandwidth is necessary in order to achieve reliability in the detection of diamond in a material stream. The skilled person knows that using a smaller bandwidth means that the method risks missing diamonds that, due to various reasons, may have a slightly different spectral peak than those which the diamond detector is arranged to detect.